Such equipment is used in the field for telephonic transmissions both at the level of telecommunications such as the antennas for the GSM (Global System for Mobil Communications) and PCS (Personal Communications Services) systems, and more generally for wireless telephonic transmissions that other present or future technologies would require for aerial connections.
Known in the state of the art are various mast and tower solutions intended for telephonic transmission. Also known are telescopic masts whose essential value is to enable a tapering structure that conserves optimal wind resistance.
As an example, French patent FR 2,745,423 describes an antenna support comprising two parallel braces articulated close to each other by one end at the base of a rigid support, and attached to a vertical mast so as to form a quadrilateral deformable in the vertical plane so as to regulate the slope of the antenna.
WO 98/58420 pertains to a cellular site mast assembly that is integrated with various antennas and constituted such that the assembly is easy to install on a cellular site without having to use extensive or analogue cabling. The assembly also comprises a light glass fiber housing which surrounds the antenna without disturbing its operation. The assembly presents a balancing system that allows raising or lowering the housing in order to gain access to the antenna.
WO 99/66589 describes an antenna configuration intended to be used particularly with a cellular telephone system in a rural environment. This antenna apparatus comprises a hollow steel support column covered by a hollow glass-fiber-reinforced plastic sheath, for example. The support column and the sheath are designed so as to present an exterior appearance simulating the bark of a tree such as a Scotch pine. The column is bolted to a concrete base placed below ground level and presents a cover simulating tree roots. The sheath carries and covers an omnidirectional antenna attached to a feed line passing through the column and the conduit located inside the concrete base. The equipment compartment of a base station of the cellular telephone system is connected to the antenna feed line.
European patent EP 106,069, entitled “Telescopic mast intended to support an antenna” provides for the pneumatic adjustment of telescopic tubes, the value of which is that it can be installed very quickly on the site and it is very compact.
European patent EP 57,002, entitled “Telescopic antenna mast” describes an apparatus whose value is solely to provide a telescopic system for devices at very elevated heights.
In these support systems, emphasis is generally on the greatest rigidity so as to maintain the most perfect aiming, a characteristic that increases in importance as the frequency of the transmissions increases and the spacing between supports increases. In fact, an increase in the frequency means a greater directivity of the radiation (propagation tending towards an optical behavior) and consequently the requirement of greater precision in the transmission. Without this precision, the communication coverage is faulty and the network can even fail.
The consequence is that high rigidity of the supports generally results in a more robust constitution, and therefore the use of more materials of higher quality.
To compensate for the expenses generated by the requirement for larger and heavier towers, the current practice, especially in the case with which we are concerned in the present typically for GSM support towers, is to use a trellis system constituted of portions of metal profiles riveted and/or welded to each other. The calculations for this metal construction start from specifications that indicate notably the resistance to weather, e.g., deformation by wind, so as to ensure the operations of the network and communication coverage. As an indication, for GSM the value of the aim loss must not exceed 20′ in the case of strong winds.
The present increasingly widespread use of mobile telephones and the services that are and will be associated with them (e.g., access to databases and the Internet) means that the requirements for antenna support towers are becoming more important and simultaneously imposing problems of the material and fabrication costs of these supports, the time required for their preparation as well as their transport, their assembly and their installation. In urban areas particularly, so as to ensure that users have perfect coverage, installers tend to mount their antennas on the roofs of the tallest buildings, which creates numerous attachment problems, since the present supports, due to the required rigidity, require extensive bracing.
Finally, in terms of the environment, the present proliferation of GSM towers of a certain volume threatens to disfigure the landscape. The state of the art in antenna support towers reveals, in addition to the desire to reduce the bulk of these systems, other fundamental requirements such as rapidity of assembly, decrease in the drag, more rapid attachments and resistance to vandalism (case of isolated posts). The impact of a decrease in weight affects not only the cost of the raw materials but also the transport cost and the cost of the material for its implementation.